The invention concerns a radio-controlled timepiece which receives radio signals for correcting, if necessary, the time display (e.g., the indicating hands).
A radio-controlled timepiece of that kind is known from European Patent No. 0 531 853, wherein an electromagnetic antenna has a core that carries a coil. The coil operates a receiver for receiving external radio signals which correct the position of the time indicating hands if the position thereof does not correspond to the correct time represented by the radio signal. The core acts as a carrier for circuitry and display components. In the interests of providing for a compact structure, in particular in the form of a radio-controlled wristwatch, a thin disc-shaped core of the magnetic long-wave antenna itself (which is separate from the core portion which functions as the coil carrier), serves so-to-speak as a mechanism plate. Mounted thereon and, as far as may be necessary extending into same, is the mechanism comprising gears and hands, including the electromotor stepping drive thereof, as well as the electronic circuits for autonomous timepiece operation and for items of display correction information which are obtained fran received and decoded time signals. Also fitted into the shallow thin core is a receiving region for an electro-optical digital display. In order to reduce the machining expenditure on the ferrite core, miniaturized precision moldings of plastic material can be fitted into the core, for the gear mechanism bearing means.
A problem which arises with such a design is the proximity on the one hand of the electronic evaluation circuit and on the other hand the electromechanical hands drive in relation to the magnetic long-wave antenna in the form of the core with its antenna coil, since electromagnetic disturbances originating from the electronic and electromechanical circuits can be fed back in augmented form by way of the antenna action. Therefore, to provide an interference-free mode of operation, the endeavor is to operate a timepiece of that construction with an increased reception field strength, which however limits the area of use in terms of the distance from the time signal transmitter. Particularly critical are electrical interference phenomena which are due to operation of the voltage transformer circuit for the actuation of an LCD-display because the clock for the voltage transformer, which is derived from the frequency divider of the autonomous time-keeping circuit of the timepiece, with a strong harmonic, lies typically in the immediate vicinity of the transmission frequency of 77.5 kHz of the German time transmitter DCF77. As a result, the reception signal can be so heavily overlaid that the information in the received time signal can no longer be evaluated at all. However the clock-controlled currents in the processor for controlling the timepiece functions also give rise to alternating magnetic fields which cause heavy interference. The installation of electromagnetic shielding boxes between the antenna and the interference-radiating mans mounted on the antenna core would not only be very expensive from a production point of view but would also result in severe damping of the antenna so that the minimum field strength at the place of reception, required for interference-free operation of the timepiece, would further increase.
In consideration of those factors the object of the invention is so to design a radio-controlled timepiece of the general kind set forth that, without major additional structural expenditure and without the antenna effectiveness being unreasonably impaired, effective suppression of the electromagnetic interference influences from operating components which operate in the immediate vicinity of the antenna core itself is guaranteed.